Polyphosphazenes (PP) are a class of versatile materials that can be functionalized with a variety of bioactive substituents including steroids, carbohydrates, amino acid esters, <i>etc</i>. These materials are typically biocompatible and biodegradable, producing non-toxic and non-acidic degradation products. Thus, substituted PPs have been studied for a variety of biomedical applications ranging from drug delivery to tissue engineering. However, the synthesis of the respective polymers still presents a challenge relative to more conventional degradable biomaterials. The classical approach to prepare PPs starts with the ring opening polymerization of the cyclic trimer hexachlorocyclotriphosphazene to poly(dichlorophosphazene) under inert conditions at high temperature, followed by purification of the product and nucleophilic substitution at the phosphorus atom. The process is cumbersome and affords materials with high polydispersity. We have recently developed a variation on this approach by allowing the ring opening polymerization to occur to a limited extent under non-inert atmosphere in an airtight container. This was followed by a one-step substitution with a single amino acid ester hydrochloride or a mixture of two esters, to afford co-substituted poly[(amino acid ester)phosphazene]s. Three functional PPs were prepared, substituted with 10 mol % glutamic acid and 90 mol % alanine, phenylalanine or methionine, respectively. Adequate molecular weights (160 – 300 kDa) and low polydispersity (PDI = 1.3 to 1.8) were achieved. The materials were biocompatible, showing no cytotoxicity towards fibroblasts in both metabolic activity using MTT and confocal microscopy studies. Furthermore, while successful electrospinning of the pure materials was difficult, a blend with 50 wt. % polycaprolactone produced relatively uniform fiber diameters with a bead-free morphology and good porosity. Further research will focus on scaffold preparation using the co-substituted poly[(amino acid ester)phosphazene]s for application in vascular tissue engineering.

Functional co-substituted poly[(amino acid ester)phosphazene] biomaterials for vascular tissue engineering

254th National Meeting (2017)

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